1. Field of the Invention
The present invention relates to an image recording apparatus for performing a scanning exposure of an image to the sheet printing plate material and the printing plate of plastic support.
2. Description of the Related Art
In earlier development, an image recording apparatus is disclosed, where a sheet printing plate material of a plastic support or a printing plate is wound on a surface of a drum, and the drum is rotated to perform scanning exposure of an image data with a light source so that an image is recorded.
In a recording apparatus for an aluminum printing material, a reflectance on a surface of a drum is not mentioned because aluminum itself does not transmit light. Further, in a recording apparatus for film or paper, reflection density only in visible light range has been mentioned.
There are following problems in performing scanning exposure of an image data with a light source using the sheet printing plate material or printing plate having a plastic support so that an image is recorded.
Firstly, in the case of the sheet printing plate material of plastic support, it has transparency of infrared light used for an exposure, compared to the aluminum printing material, or film or paper. Thus, light which has not been converted to heat at a thermosensitive image forming layer is transmitted through the plastic support, and is reflected on a surface of a drum so as to react at the thermosensitive image forming layer again, so that the image density increases more than necessary.
Secondly, when some concavoconvex such as clamp groove, suction groove and peel groove is formed on a surface of the drum of the image recording apparatus, density nonuniformity occurs since the distance between the bottom of the groove and the plastic support is different from the distance between the surface of the drum and the plastic support and a reaction on the thermosensitive image forming layer varies.
Thirdly, when backside of the plastic support is colored so as not to transmit infrared light, the backside is heated due to the coloring and density nonuniformity occurs in the thermosensitive image forming layer since the heat transmittances are different between metal of the surface of the drum and the air layer of the groove.